A flow distribution plate and an engine exhaust gas aftertreatment device comprising such a plate

ABSTRACT

The invention relates to a flow distribution plate associated with an engine exhaust gas aftertreatment device, wherein the plate is perforated and is adapted to be arranged at an inlet to an exhaust gas purifying unit to improve the flow distribution of exhaust gas into the purifying unit. The flow distribution plate is curved in relation to the inlet, such that a more uniform flow velocity distribution is achieved over the inlet. The invention also relates to an engine exhaust gas aftertreatment device and a vehicle comprising such an engine exhaust gas aftertreatment device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application (filed under 35 § U.S.C. 371) of PCT/SE2017/050450, filed May 8, 2017 of the same title, which, in turn, claims priority to Swedish Application No. 1650722-0, filed May 25, 2016; the contents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a flow distribution plate associated with an engine exhaust gas aftertreatment device, an engine exhaust gas aftertreatment device and a vehicle comprising such a device.

BACKGROUND OF THE INVENTION

Exhaust gas aftertreatment systems for engines are commonly known and are used to remove or reduce undesired constituents from the exhaust gas before it is discharged into the environment. An exhaust gas aftertreatment system may comprise different types of purifying units for removing these undesired constituents, such as a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) catalyst. In order to optimize the performance of a purifying unit, and thus to remove as much constituents as possible, it is important to achieve an optimal flow distribution into the purifying unit. A perforated flow distribution plate may be arranged at the inlet to the purifying unit to improve the flow distribution. In serially connected exhaust gas aftertreatment systems, which are configured such that the inflow of exhaust gas is essentially perpendicularly to the plane of the inlet of the purifying unit, a somewhat even flow over the perforated plate is achieved and the plate is very effective in distributing the exhaust gas over the inlet of the purifying unit. On vehicles today, however, space is limited and exhaust gas aftertreatment systems are therefore configured as very compact systems. This often results in exhaust pipes with sharp bends and the inflow of exhaust gas may be parallel with the plane of the inlet to the purifying unit. This results in an uneven flow over the perforated plate, and the ability of the plate to improve the flow distribution is therefore deteriorated. The efficiency and performance of the purifying unit is thereby impaired.

Various solutions exist for improving the efficiency of a perforated flow distribution plate and thus improving the flow distribution into a purifying unit. Document EP2664756 A2, for example, discloses a diesel engine exhaust gas aftertreatment device comprising a DOC, where a baffle with perforations is arranged in front of the DOC to facilitate a uniform distribution of exhaust gas. The perforations of the baffle are formed at different densities at different areas, such that a uniform flow distribution into the DOC may be obtained. Document JP2010159719 A discloses an exhaust gas aftertreatment device where a perforated plate is arranged between a bent pipe part and the inlet to a catalyst. The perforations are different in size, and the perforations closest to the bend are larger than the other perforations. This way, a more uniform flow distribution over the inlet to the catalyst is obtained.

SUMMARY OF THE INVENTION

Despite known solutions in the field, there is still a need to develop a flow distribution plate associated with an engine exhaust gas aftertreatment device, which improves the ability to obtain a more uniform flow distribution over the inlet to a purifying unit and thus improves the efficiency and performance of the purifying unit.

An object of the present invention is to achieve an advantageous flow distribution plate associated with an engine exhaust gas aftertreatment device, which plate is configured to affect a flow of exhaust gas, such that a higher uniformity index is obtained over an inlet to a purifying unit.

An object of the present invention is to achieve an advantageous flow distribution plate associated with an engine exhaust gas aftertreatment device, which plate improves the efficiency and performance of a purifying unit of the exhaust gas aftertreatment device.

Another object of the present invention is to achieve an advantageous engine exhaust gas aftertreatment device, which is configured to affect a flow of exhaust gas, such that a higher uniformity index is obtained over an inlet to a purifying unit.

A further object of the present invention is to achieve an advantageous engine exhaust gas aftertreatment device, which improves the efficiency and performance of a purifying unit of the exhaust gas aftertreatment device.

The herein mentioned objects are achieved by a flow distribution plate associated with an engine exhaust gas aftertreatment device, an engine exhaust gas aftertreatment device, and a vehicle comprising such a device according to the independent claims.

According to an aspect of the present invention, a flow distribution plate associated with an engine exhaust gas aftertreatment device is provided. The plate is perforated and is adapted to be arranged at an inlet to an exhaust gas purifying unit to improve the flow distribution of exhaust gas into the purifying unit. The plate is furthermore curved in relation to the inlet, such that a more uniform velocity distribution can be achieved over the inlet.

Flat, perforated flow distribution plates, baffles or similar are often arranged in front of inlets to purifying units in order to improve the flow distribution into the purifying unit. This way, the performance of the purifying unit is improved. Depending on how the exhaust gas is conducted to the purifying unit, the flow over the flow distribution plate may vary. If the exhaust gas is conducted to the purifying unit such that an uneven flow is provided over such a known flat flow distribution plate, the functionality of the flow distribution plate will be deteriorated. The flow distribution plate according to the invention, herein also called the plate, is suitably adapted to be arranged in front of the inlet to the purifying unit in order to improve the flow distribution over the inlet and thus the flow into the purifying unit. The flow distribution plate is suitably configured with a curvature adapted to handle an uneven flow over the plate. How the exhaust gas is conducted to the purifying inlet, and thus the flow over the flow distribution plate, is determined by the configuration of the exhaust gas aftertreatment device in which the perforated plate is adapted to be arranged. By configuring the flow distribution plate according to the invention with a curvature, the curvature will affect the flow resistance at the plate such that the original flow direction of the exhaust gas will be affected. The exhaust gas will always choose to flow where there is least resistance. A more uniform flow velocity distribution may thereby be achieved over the inlet to the purifying unit. In addition, by configuring the flow distribution plate with a curvature the distance between the plate surface and the inlet to the purifying unit will vary. A curved flow distribution plate will thus result in some areas where it is a greater distance between the plate surface and the inlet. An area where the distance between the inlet and the flow distribution plate is greater thus constitutes a protruding portion. The exhaust gas encountering the protruding portion will flow next to the protruding portion since the flow resistance is less than to flow through the perforations in the flow distribution plate. The mass flow and the velocity through such a protruding portion will thereby decrease. The curvature will thereby result in that a larger mass flow passes through the perforations of the flow distribution plate where the distance to the inlet is smaller. The shape of the curvature of the plate thus determines how mass flow is directed to different areas of the plate. In addition, the curvature of the flow distribution plate results in that the axial direction of the perforations in the plate varies over the plate surface. This way, the flow direction of the exhaust gas entering the purifying unit varies and a more uniform flow distribution of exhaust gas into the purifying unit may thereby be achieved.

The flow distribution plate thickness may be between 3-7 millimetres. The plate is suitably made of metal, such as steel. The flow distribution plate suitably has a shape corresponding to the shape of the inlet to the purifying unit. The inlet to the purifying unit may be circular and the flow distribution plate is thereby suitably circular.

The flow distribution plate is suitably adapted to be arranged in an exhaust gas aftertreatment device with an exhaust gas pipe, which opens into a volume called end cap. The end cap is suitably arranged at an end of the purifying unit comprising the inlet, and the end cap thus encloses the inlet of the purifying unit. The flow distribution plate is thus suitably adapted to be arranged at the interface between the purifying unit and the end cap.

The flow distribution plate suitably comprises attachment means for attaching the plate to the inner wall of the end cap or the inner wall of the purifying unit. The attachment means may comprise a plurality of bodies symmetrically arranged along the circumference of the flow distribution plate. The attachment means may alternatively be one circumferentially arranged body. The curvature of the flow distribution plate may be configured such that a cross-section of the plate will show the attachment means offset. That is, the curvature may be configured such that the attachment means at different parts of the plate is at different distance from the inlet of the purifying unit when the plate is correctly arranged. The curvature may thus be configured such that the attachment means are in different planes.

According to an aspect of the invention, the curvature of the flow distribution plate is shaped depending on the direction of the inflow of exhaust gas in relation to the inlet of the purifying unit. As previously mentioned, the flow over the flow distribution plate determines the ability of the plate to improve the exhaust gas flow distribution into the purifying unit. Different directions of incoming exhaust gas will cause different flow over the flow distribution plate. The curvature of the flow distribution plate thus suitably depends on the direction of the inflow of exhaust gas, in relation to the inlet of the purifying unit. The curvature of the flow distribution plate may thus depend on the incoming flow of exhaust gas over the flow distribution plate. The curvature may also depend on the geometry of the exhaust gas pipe and the end cap leading the exhaust gas to the purifying unit.

The exhaust gas flow generated by the engine depends on the engine speed. When the exhaust gas flow is low, the curvature of the flow distribution plate may not significantly affect the flow velocity distribution but when the exhaust gas flow is high, the curvature may be very important. The curvature of the flow distribution plate may thus be based on an average exhaust gas flow provided by the engine.

According to an aspect of the invention the curvature of the flow distribution plate is asymmetric, such that the maximum or minimum point of the curvature is different from the center point of the plate. This way, the curvature of the flow distribution plate may be better adapted after the incoming direction of the exhaust gas flow, such that a more uniform velocity distribution over the inlet is achieved. Alternatively, the flow distribution plate is essentially convex in relation to the inlet of the purifying unit. The flow distribution plate is suitably curved such that the incoming exhaust gas with the highest flow velocity hits a part of the flow distribution plate, which is furthest away from the inlet to the purifying unit. That is, the curvature is suitably such that the exhaust gas with the highest velocity first encounters a part of the flow distribution plate, which protrudes away from the inlet of the purifying unit. This way, the protruding part will affect the flow velocity distribution in an efficient way and a more uniform flow velocity distribution over the inlet to the purifying unit is achieved.

According to an example, the exhaust gas aftertreatment device comprises an exhaust gas pipe which is arranged such that the inflow of exhaust gas to the end cap is essentially parallel with the plane of the inlet to the purifying unit. The exhaust gas aftertreatment device is thus configured such that it provides a lateral inflow of exhaust gas and the flow over the flow distribution plate is uneven. If the exhaust gas pipe has a small diameter, the flow resistance is higher and the velocity of the exhaust gas must be increased in order to provide the purifying unit with the same mass flow of exhaust gas. If the flow distribution plate was flat as commonly known, most of the exhaust gas would, due to the high velocity, flow straight ahead to the end of the end cap and subsequently enter through the perforations of the plate at that end. The flow velocity distribution over the inlet would thereby be non-uniform. Wth a flow distribution plate according to the invention, the curvature would obstruct some of the exhaust gas, the flow resistance would thereby be affected, the exhaust gas flow would be distributed over the flow distribution plate and a higher uniformity index over the inlet would be obtained.

According to an aspect of the invention, the flow distribution plate comprises a first portion protruding away from the purifying unit, and a second portion, which is essentially parallel with the plane of the inlet. The protruding portion may be an essentially convex portion. The flow distribution plate may comprise one or more protruding portions. The protruding portions may have different radii. The flow distribution plate may comprise one or more concave portions in relation to the inlet. A concave portion is thus protruding towards the purifying unit and may be perceived as a recess by the incoming exhaust gas.

The perforations of the flow distribution plate are suitably of essentially equal size. The perforations may have a diameter between 2-10 millimetres. The perforations are furthermore suitably essentially evenly distributed over the surface of the flow distribution plate. This way, the flow distribution plate can be manufactured in an easy and time efficient way. The flow distribution plate can thereby be achieved in a more cost effective way compared to known prior art.

According to an aspect of the invention, an engine exhaust gas aftertreatment device is provided. The engine exhaust gas aftertreatment device comprises at least one exhaust gas purifying unit with an inlet. A perforated flow distribution plate is arranged at the inlet to the purifying unit, to improve the flow distribution of exhaust gas into the purifying unit. The flow distribution plate is curved in relation to the inlet, such that a more uniform velocity distribution can be achieved over the inlet. The exhaust gas aftertreatment device suitably comprises an exhaust gas pipe arranged in fluid communication with the engine and a volume called end cap. The end cap is suitably arranged at the end of the purifying unit comprising the inlet and the end cap thus encloses the inlet of the purifying unit. The flow distribution plate is thus suitably arranged at the interface between the purifying unit and the end cap. The exhaust gas pipe may open into the end cap from any direction, which thus affects the exhaust gas flow over the perforated flow distribution plate.

According to an aspect of the invention, the purifying unit is a selective catalytic reaction catalyst (SCR). The purifying unit may alternatively be a diesel particle filter (DPF) or a diesel oxidation catalyst (DOC) The device is suitably a compact exhaust gas aftertreatment device and may be adapted to be integrated with a silencer in a vehicle.

According to an aspect of the invention, the exhaust gas aftertreatment device is configured such that the flow direction of the exhaust gas approaching the inlet is essentially parallel with the plane of the inlet. The exhaust gas pipe is thus suitably arranged such that it opens into the end cap in parallel with the plane of the inlet.

According to an aspect of the invention, the exhaust gas aftertreatment device is configured such that the flow direction of the exhaust gas approaching the inlet is directed with an angle in relation to the plane of the inlet, wherein the angle is between 0-80 degrees. The exhaust gas pipe is thus suitably arranged such that it opens into end cap with an angle in relation to the plane of the inlet, wherein the angle is between 0-80 degrees.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various drawings, and in which:

FIG. 1 schematically illustrates a vehicle according to an embodiment of the invention;

FIG. 2 schematically illustrates an engine exhaust gas aftertreatment device according to an embodiment of the invention;

FIG. 3a-3d schematically illustrates the difference in flow velocity distribution between prior art and a flow distribution plate according to an embodiment of the invention;

FIG. 4a-4b schematically illustrates a flow distribution plate according to embodiments of the invention; and

FIG. 5 schematically illustrates a flow distribution plate according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a side view of a vehicle 1 comprising an engine 2 and an engine exhaust gas aftertreatment device 10 connected to the engine 2, The engine 2 may be an internal combustion engine or any other engine generating exhaust gas. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car. The vehicle may be manually operated, remotely operated or autonomously operated.

FIG. 2 shows an engine exhaust gas aftertreatment device 10 according to an embodiment of the invention. The engine exhaust gas aftertreatment device 10 is suitably associated with an engine 2 in a vehicle 1 as described in FIG. 1. The device 10 is a compact exhaust gas aftertreatment device and may be integrated in a silencer. The device 10 suitably comprises an exhaust gas pipe 20 connected to the engine 2, a purifying unit 30 and an end cap 40 connecting the purifying unit 30 and the exhaust gas pipe 20. The purifying unit 30 may be a selective catalytic reaction catalyst (SCR), a diesel particulate filter (DPF) or a diesel oxidation catalyst (DOC). The purifying unit 30 comprises an inlet 32 through which exhaust gas enter the purifying unit 30. The purifying unit 30 suitably comprises a substrate with channels through which the exhaust gas is conducted. The channels suitably extend perpendicularly to the plane of the inlet 32. The exhaust gas exits the purifying unit at an end opposite to the inlet 32. The efficiency of the purifying unit 30 depends on the flow distribution over the inlet 32 and thus the flow distribution into the purifying unit 30. A flow distribution plate 34 is arranged in front of the inlet 32 in order to improve the flow distribution over the inlet 32. The end cap 40 is arranged such that it encloses the inlet 32 to the purifying unit 30 and the flow distribution plate 34 is arranged between the end cap 40 and the inlet 32 to the purifying unit 30. The exhaust gas thus flow from the engine 2 via the exhaust gas pipe 20 to the end cap 40 and through the flow distribution plate 32 into the purifying unit 30. The exhaust gas may then be conducted to a further purifying unit or it may be discharged into the environment. The flow direction of the exhaust gas is illustrated by arrows.

The end cap 40 is a volume into which exhaust gas is conducted from the engine 2 via the exhaust gas pipe 20. The exhaust gas pipe 20 may open into the end cap 40 from any direction, which affects the exhaust gas flow distribution over the perforated flow distribution plate 34. In this example, the exhaust gas pipe 20 is arranged such that it enters the end cap 40 essentially in parallel with the plane of the inlet 32. The exhaust gas pipe 20 may alternatively be arranged such that it enters the end cap 40 with an angle in relation to the plane of the inlet 32, wherein the angle is between 0-85 degrees.

The flow distribution plate 34 is curved in relation to the inlet 32, such that a more uniform velocity distribution can be achieved over the inlet 32. This way, the performance and efficiency of the purifying unit 30 is improved. The flow distribution plate 34 may have a circular shape and may be between 3-7 millimetres thick. The plate 34 is suitably made of metal, such as steel. The flow distribution plate 34 suitable comprises attachment means 36 arranged along the circumference of the flow distribution plate 34. The attachment means 36 is attached to the inner wall of the end cap 40 or the inner wall of the purifying unit 30. The curvature of the flow distribution plate 34 may be configured such that a cross-section of the plate 34 will show the attachment means 36 offset. That is, the curvature may be configured such that the attachment means at different parts of the flow distribution plate 34 is at different distance from the inlet 32 of the purifying unit 30 when the plate 34 is correctly arranged. The curvature of the flow distribution plate 34 is suitably formed depending on the direction of the inflow of exhaust gas in relation to the inlet 32. The flow over the flow distribution plate 34 determines the ability of the plate 34 to improve the exhaust gas flow distribution into the purifying unit 30. The curvature of the flow distribution plate 34 is thus suitably adapted to the direction of the inflow of exhaust gas, in relation to the inlet 32. The curvature may also depend on the geometry of the exhaust gas pipe 20 and the end cap 40 leading the exhaust gas to the purifying unit 30. The curvature of the flow distribution plate 34 may be asymmetric, such that the maximum or minimum point of the curvature is different from the center point of the plate 34. The flow distribution plate 34 may be curved such that the incoming exhaust gas with the highest flow velocity hits a part of the flow distribution plate 34, which is furthest away from the inlet 32 to the purifying unit 30. This way, a more uniform velocity distribution over the inlet 32 is achieved.

The perforations 38 of the flow distribution plate 34 are suitably of essentially equal size. The perforations 38 may have a diameter between 7-10 millimetres. The perforations 38 are furthermore suitably evenly distributed over the surface of the flow distribution plate 34.

FIG. 3a-3d schematically illustrates the difference in flow velocity distribution between prior art and a flow distribution plate 34 according to an embodiment of the invention. The figures thus illustrate the function of a flow distribution plate 34 according to an embodiment of the invention. FIG. 3a illustrates the exhaust gas flow in an exhaust gas aftertreatment device 10 comprising a commonly known flat flow distribution plate 34′. The figure shows exhaust gas entering an end cap 40 from the right, via an exhaust gas pipe 20 with small diameter at the inlet to the end cap 40. Due to the small diameter of the exhaust gas pipe 20 the flow velocity of the exhaust gas entering the end cap 40 is high. Wth a flat flow distribution plate 34′, the exhaust gas avoids the resistance caused by the plate 34′ and flows straight ahead, i.e. to the left in the figure, to the end of the end cap 40. At this stage, some exhaust gas will pass through the flow distribution plate 34′ but some of the exhaust gas will flow to the right in the figure, where the pressure is lower and the resistance thus is smaller. A backflow thus occurs and turbulence is created which is illustrated with arrows directed to the right in the figure. FIG. 3b illustrates the flow velocity distribution over the inlet 32, thus after the exhaust gas has passed through the flat flow distribution plate 34′. The flow velocity is highest at the far left of FIG. 3a which is illustrated with a black area in FIG. 3b . The flow velocity decreases closer to the opening of the exhaust gas pipe 20, which is illustrated with the two patterned areas. The laminar flow of a fluid in a closed pipe gives a velocity profile where the velocity is higher in the center of the flow and lower closer to the walls of the pipe. The area with the lowest flow velocity is thus close to the bend after the opening of the exhaust gas pipe 20. This is illustrated as a white area. The somewhat increased velocity closest to the bend is caused by the backflow mentioned above. As illustrated in FIG. 3b , a flat flow distribution plate 34′ will result in a very non-uniform flow velocity distribution over the inlet 32 to the purifying unit 30.

FIG. 3c illustrates exhaust gas flow in an exhaust gas aftertreatment device 10 according to FIG. 2. The figure shows exhaust gas entering an end cap 40 from the right, via an exhaust gas pipe 20 with small diameter at the inlet to the end cap 40. Due to the small diameter of the exhaust gas pipe 20 the flow velocity of the exhaust gas entering the end cap 40 is high. In this example, the flow distribution plate 34 comprises an asymmetric curvature, with a protruding portion, which obstructs the exhaust gas flow. The protruding portion increases the flow resistance between the end cap wall 40 and the protruding portion and exhaust gas with higher velocity will choose to flow directly to the right when entering the end cap 40. The protruding portion results in a greater distance between the plate surface and the inlet 32. Lower mass flow and velocity will thereby be obtained through the perforations 38 of the protruding portion and increased mass flow will pass through the perforations 38 where the distance to the inlet 32 is smaller. FIG. 3d illustrates the flow velocity distribution over the inlet 32 with a flow distribution plate 34 according to FIG. 3c . The flow velocity is the highest to the left in FIG. 3 c which is illustrated with a black area in FIG. 3d . The flow velocity decreases closer to the opening of the exhaust gas pipe 20 which is illustrated with the two patterned areas. The curvature of the flow distribution plate 34 thus affects the flow resistance and thereby results in a more uniform flow velocity distribution over the inlet 32 to the purifying unit 30 compared to the flat flow distribution plate 34′ in FIG. 3a . The performance and efficiency of the purifying unit 30 is thereby improved.

FIGS. 4a and 4b schematically illustrates two examples of flow distribution plates 34 in an engine exhaust aftertreatment device 10 according to the invention, with different types of curvature. The engine exhaust gas aftertreatment device 10 is suitably configured as described in FIG. 2 and is in both FIG. 4a and FIG. 4b configured such that an uneven flow is obtained over the flow distribution plate 34. The exhaust gas pipe 20 is arranged such that the incoming exhaust gas is directed with an angle to the plane of the inlet 32 to the purifying unit 30. The angle may be between 0-80 degrees. In this example the angle is about 50 degrees. The exhaust gas flow is illustrated with arrows.

FIG. 4a shows a flow distribution plate 34 with an asymmetric curvature. The curvature comprises a portion protruding away from the inlet 32, with a maximum point close to where the exhaust gas pipe 20 opens into the end cap 40. The curvature of the flow distribution plate 34 thus results in that the distance between the plate surface and the inlet 32 of the purifying unit 30 is increased where the exhaust gas is entering the end cap. The flow resistance is thereby affected and a more uniform flow velocity distribution over the inlet 32 is achieved.

FIG. 4b shows a flow distribution plate 34 with an asymmetric curvature comprising a first portion protruding away from the inlet 32 and a second portion protruding towards the inlet 32. The curvature thus includes an essentially convex portion and an essentially concave portion in relation to the inlet 32. The flow distribution plate 34 thus comprises a portion resulting in a greater distance between the plate surface and the inlet 32 and a portion resulting in a smaller distance between the plate surface and the inlet 32. This way, the flow resistance is affected and a more uniform flow velocity distribution over the inlet 32 is achieved.

FIG. 5 schematically illustrates a flow distribution plate 34 in an engine exhaust aftertreatment device 10 according to an embodiment of the invention. The engine exhaust gas aftertreatment device 10 is configured with an exhaust gas pipe 20 arranged essentially perpendicularly to the plane of the inlet 32 to the purifying unit 30. The flow distribution plate 34 is curved in relation to the inlet 32. The curvature is essentially convex in relation to the inlet 32. The velocity profile of the exhaust gas flow entering the end cap 40 will be such that the velocity is higher in the center of the flow and lower at the sides. The curvature of the flow distribution plate 34 will thus make the exhaust gas with the highest velocity flow toward the sides of the end cap 40 and a more uniform flow velocity distribution of the inlet 32 is thereby achieved.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use. 

1. A flow distribution plate associated with an engine exhaust gas aftertreatment device, wherein the plate is perforated and is adapted to be arranged at an inlet to an exhaust gas purifying unit to improve the flow distribution of exhaust gas into the purifying unit, wherein the flow distribution plate is curved in relation to the inlet, such that a more uniform flow velocity distribution is achieved over the inlet, wherein the curvature of the flow distribution plate is asymmetric and formed depending on the direction of the inflow of exhaust gas in relation to the inlet, wherein the flow distribution plate is curved such that the incoming exhaust gas with the highest flow velocity hits a part of the flow distribution plate, which is furthest away from the inlet to the purifying unit.
 2. The plate according to claim 1, wherein the perforations of the flow distribution plate are of essentially equal size.
 3. The plate according to claim 1, wherein the perforations of the flow distribution plate are evenly distributed over the surface of the plate.
 4. The plate according to claim 1, wherein the plate comprises an essentially convex portion in relation to the inlet.
 5. An engine exhaust gas aftertreatment device, comprising at least one exhaust gas purifying unit with an inlet, wherein a flow distribution plate is arranged at the inlet of the purifying unit, wherein said flow distribution plate wherein the plate is perforated and is adapted to be arranged at an inlet to an exhaust gas purifying unit to improve the flow distribution of exhaust gas into the purifying unit, wherein the flow distribution plate is curved in relation to the inlet, such that a more uniform flow velocity distribution is achieved over the inlet, wherein the curvature of the flow distribution plate is asymmetric and formed depending on the direction of the inflow of exhaust gas in relation to the inlet, wherein the flow distribution plate is curved such that the incoming exhaust gas with the highest flow velocity hits a part of the flow distribution plate, which is furthest away from the inlet to the purifying unit.
 6. The device according to claim 7, wherein the purifying unit is a selective catalytic reaction catalyst.
 7. The device according to claim 5, wherein the device is adapted to be integrated with a silencer of a vehicle.
 8. The device according to claim 5, wherein the device is configured such that the inflow of exhaust gas to the inlet is essentially parallel with the plane of the inlet.
 9. The device according to claim 5, wherein the device is configured such that the inflow of exhaust gas to the inlet is directed with an angle in relation to the plane of the inlet, wherein the angle is between 0-80 degrees.
 10. A vehicle comprising an engine exhaust gas aftertreatment device comprising at least one exhaust gas purifying unit with an inlet, wherein a flow distribution plate is arranged at the inlet of the purifying unit, wherein said flow distribution plate wherein the plate is perforated and is adapted to be arranged at an inlet to an exhaust gas purifying unit to improve the flow distribution of exhaust gas into the purifying unit, wherein the flow distribution plate is curved in relation to the inlet, such that a more uniform flow velocity distribution is achieved over the inlet, wherein the curvature of the flow distribution plate is asymmetric and formed depending on the direction of the inflow of exhaust gas in relation to the inlet, wherein the flow distribution plate is curved such that the incoming exhaust qas with the highest flow velocity hits a part of the flow distribution plate, which is furthest away from the inlet to the purifying unit.
 11. The vehicle according to claim 10, wherein the purifying unit is a selective catalytic reaction catalyst.
 12. The vehicle according to claim 10, wherein the device is adapted to be integrated with a silencer of a vehicle.
 13. The vehicle according to claim 10, wherein the device is configured such that the inflow of exhaust gas to the inlet is essentially parallel with the plane of the inlet.
 14. The vehicle according to claim 10, wherein the device is configured such that the inflow of exhaust gas to the inlet is directed with an angle in relation to the plane of the inlet, wherein the angle is between 0-80 degrees.
 15. The plate according to claim 1, wherein the plate comprises an essentially concave portion in relation to the inlet. 